Noise under my brake pedal!

[SHOstuff]

I'm having a noise come from under my brake pedal like a hissing noise. When I press the pedal it quiets a little bit but you get still hear it. And I'm trying to figure it out, is it because I have one of my brake sensors unplugged? headbang

 

[jasonty]

This sounds a lot like a bad brake booster to me. Push the pedal to the floor, if it makes a "whooshing" sound, you most likely have a bad booster. If that isn't it, unplug the check valve from the booster (the valve connected to the vacuum line on the brake booster in the engine bay) and try blowing through it. You should only be able to blow through it one way. Good luck!